Dihalides trans

Brown, J. K., and N. Sheppard Infrared spectroscopic studies of rotational isomerism. I. The assignment of the fundamental frequencies of some ethylene dihalides. Trans. Faraday Soc. 48, 128—137 (1952). 

When the halogenation reaction is carried out on a cycloalkene, such as cyclopentene, only the trews stereoisomer of the dihalide addition product is formed rather than the mixture of cis and trans isomers that might have been expected if a planar carbocation intermediate were involved. We say that the reaction occurs with anti stereochemistry, meaning that the two bromine atoms come from opposite faces of the double bond—one from the top face and one from the bottom face. 

Kumakov s test (1893) is generally applicable to cis- and trans-ammine dihalides. Addition of thiourea (tu, (H2N)2CS) to the cA-complex leads to successive replacement of all the ligands (Figure 3.29) here the lability of the Pt—Cl bond (see section 3.8.9) causes substitution of a chloride. 

Related to these elimination processes is the reduction of 1,4-dihalides of trans-but-2-ene in dimethylformamide to yield butadiene [137]. 

The stereochemistry of formation and rearrangement of vicinal dihalides has been elucidated, chiefly by Barton s group.221,266,267 Trans diaxial addition occurs but the product may then equilibrate with the more stable... 

Credali et al. 62-65 > prepared polypiperazineamides (75, R=trans-l,2-ethylenediyl, 2-propen- 1,2-diyl, tetramethylene, m-phenylene, p-phenylene, thiofurazanediyl (16) Rj, H or CH3 R2, H or CH3) membranes from the corresponding acyl dihalides and... 

The synthesis of 3-benzylcyclobutanone (3) is an illustration of an overall intramolecular alkylation of an acyl anion equivalent (Section 5.9). The a,a>-dihalide is 2-benzyl-l,3-dibromopropane, and the acyl anion equivalent is methyl methylthiomethyl sulphoxide2 the product is 1-methylsulphinyl-l-methylthio-3-benzylcyclobutane which is obtained as a mixture of cis/trans isomers [(9) and (10)] (Expt 7.3). Aqueous acid hydrolysis in ethereal solution unmasks the carbonyl group. The possible mechanism of the reaction is via a Stevens-type rearrangement of the intermediate sulphur ylide, which may proceed in a pericylic, radical or ion pair fashion. 

Based on the XH DNMR data1232, it is suggested that both diastereomers with either a cis or trans arrangement of the Br atoms are present in solution of dibromides 560a-b. The polytopic rearrangement in dihalides (L")2GeX2 is discussed below. 

Halogens, X2 (X = Cl or Br), add to alkynes in much the same way they add to alkenes (Section 10.13). Addition of one mole of X2 forms a trans dihalide, which can then react with a second mole of X2 to yield a tetrahalide. 

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